Ignition system for internal com



B. M; CAIN 2,100,210

IGNTTTON SYSTEM FOR INTERNAL COMBUSTION ENGTNF'YE Nov. 23, 1937.

Filed Dec. 14, 1934 u MOTOR-GENERATOR Fig. 6.

Fig 1.

Inventor. Bernar M, Cain,

by Hus Attorney.

' multi-cylinder engine.

Patented Nov. 23, 1937 UNITED STATES IGNITION SYSTEM FOR INTERNAL COM-BUSTION ENGINES Bernard M. Cain, Ballston Lake, N. Y., assignor toGeneral Electric Company, a corporation of New York Application December14, 1934, Serial No. 757,513

5 Claims.

My invention relates to ignition systems for internal combustion enginesand particularly to ignition systems wherein sparks in rapid successionare produced in the engine cylinder by a high frequency alternatingcurrent. Such a system is disclosed and claimed in the application ofMax A. Whiting, Serial No. 757,545 filed concurrently herewith. In thesystem disclosed by the above mentioned application, the high frequencyignition current is produced by a motor-generator apparatus which isdriven from a battery which also is arranged to energize the startingmotor of the engine. It is one object of my invention to provide animproved ignition system of this character whereby the voltage of thehigh frequency alternating current supplied to the spark gaps of theengine is maintained substantially uniform notwithstanding thevariations which may occur in voltage of the battery. In an ignitionsystem of this character it has been found desirable under certainconditions to provide a plurality of spark gaps in the engine cylinderor in each cylinder in the case of a It is another object of myinvention to provide an improved ignition system of this characteremploying high frequency alternating current and-providing a pluralityof spark gaps in each cylinder which system will insure that asuccession of sparks a will occur at allthe spark gaps in each cylinder.

A further object of my invention is the provision of an improvedignition system of this character in which the voltage applied to thespark gap or gaps of the engine is automatically made higher when thegap or gaps are not conducting.

My invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram representing oneembodiment of my invention and Figs. 2 and 3 show two modified forms ofthe transformers shown 'in Fig. 1. In Fig. 1, I have shown by dottedlines the internal combustion engine I which engine may be of the fuelinjection or semi-Diesel type and may have a single cylinder or may havea plurality of cylinders. I have represented the engine as afour-cylinder engine provided with the spark gaps 2, each of which maycomprise a spark plug of any suitable and well known form. Inasmuch asit has been found. that under certain conditlons improved operation isobtained by the use of a plurality of spark gaps in each cylinder, I

have shown the engine as provided with twogaps for each cylinder. Theengine also is provided with starting apparatus by means of which it maybe cranked electrically. This apparatus may be of any suitable and wellknown form including an electric motor which I have represented at 3connected through the starting switch 4 with the usual storage battery5. This battery, it will be understood, may be kept charged bybeingsupplied from a suitable generator driven from the engine in thewell known manner but as such charging means forms no part of my presentinvention it has been omitted from the drawing in order to simplify theshowmg.

Energy is taken from the battery 5, converted into high frequencyalternating current and supplied to the engine for ignition purposes.The means which I have illustrated for so converting the energy is themotor-generator ap- 'paratus 1 which may be of any suitable and wellknown form adapted to be operated from the battery 5 continuously, thatis, while the engine is running and to produce the desired highfrequency alternating current. I have found that a convenient form ofmotor-generator ap paratus is a dynamotor of the inductor type which onthe drawing is represented as having a motor element including the rotor8 and the shunt field winding 9 controlled by the rheostat l0 whichelement is connected through the switch H with the battery 5. Thedynamotor is thereby connected to the battery in shunt with the startingmotor. The generator element of the dynamotor is represented ascomprising the winding l2 which at normal operating speed of thedynamotor is constructed to produce alternating current having afrequency of the order of 2500 to 3000 cycles per second.

Connected in a series circuit with the winding l2 are the primarywindings of the step-up transformers l4 and I5 and the motor operatedswitch IS. The latter may be of any desired form and for convenience isrepresented as comprising the switch arm actuated by the cam l8 which isdriven by the engine. This switch It while represented as being of aform similar to that of the well known igniter switch of an internalcombustion engine of the common explosive type does not function in themanner of such an igniter switch since the opening of the circuit by theswitch I6 is not for the purpose of producing a spark in the enginecylinder. The purpose of the switch in the present case is to maintainthe alternating current circuit closed through those intervals onlyduring which it is desired to have a rapid succession of sparks occur inthe engine, it being noted that the time during which fuel is beinginjected into a cylinder of an engine of the injection type is only arelatively small part of the complete cycle. The secondaries of thetransformers l4 and I5 connect respectively through the distributors l9and with the spark gaps 2 whereby one transformer supplies current toone gap of each cylinder and the other transformer supplies current tothe other gap of each cylinder.

The above described apparatus is constructed.

to produce the desired voltage and frequency of the alternating currentapplied to the spark gaps when the dynamotor is supplied with the normalbattery voltage. If for any reason the battery voltage is somewhat belownormal, due for example to a partially discharged condition of thebattery or to a drop in voltage incident to the operation of thestarting motor in cranking the engine, the speed of the dynamotor willbe reduced and hence its alternating current voltage and frequency willalso be reduced. For the purpose of lessening such a decrease in thevoltage and frequency of the output of the dynamotor, I have providedthe capacitor 22 in the above-mentioned series circuit which includesthe winding l2, the transformer primaries and the switch l6, it beingunderstood that the generator winding 12 of the dynamotor is inductive.The capacitance of the capacitor 22 is so related to the inductance ofthe winding l2 that the point of resonance corresponds to a frequencyand hence to a speed of the dynamotor, which is below that speed atwhich the dynamotor ever would be d ven under proper operatingconditions. As a result of this construction it will be seen thatalthough a small decrease in speed of the dynamotor may occur due to adrop in battery voltage, the voltage applied to the transformers l4 andI5 will remain approximately the same since the impedance in the circuitof thejtransformer primaries decreases when the frequency decreases.

When dual ignition is provided for as in the present case by the twospark gaps in each cylinder it is desirable, in order to minimize thesupplied from the same source of alternating current voltage and thatthere should be a breakdown in both gaps in each cylinder.

Unlike the common single spark battery ignition systems in common usewhere the energy of the single spark is that stored in the inductioncoil employed, the energy for the rapid succession of sparks in myapparatus is supplied by the alternating current source, the supplybeing continuous during each period of sparking. For this purpose thesource of alternating current is not limited to that described above butmay comprise any suitable and well known means for producing analternating current of the desired voltage and frequency. I

Inasmuch as the resistance across a spark gap greatly decreases as soonas the gap becomes ionized due to breakdown, it is necessary that therebe a fairly large impedance in the supply circuit so as to limit theflow of current to the spark gap. With such a circuit, if the spark gapsare supplied from a single source in a parallel arrangement, one gap maybegin to conduct before the other and the current flow thereto willcause the"voltage applied to the other gap to drop due to the circuitimpedance. Hence because of the drop in voltageresulting from thebreakdown of one spark gap the second spark gap will not break down.

In accordance with another feature of my invention I have provided meansfor insuring the firing of both gaps in each cylinder. In effect, thetwo gaps of a cylinder are arranged in series. However, this is not doneby an actual series arrangement of the gaps but it is brought about byarranging the primaries of the transformers I4 and ill in series whicharrangement produces substantially the same result and avoids theotherwise necessary expedient of either a special spark plugconstruction or a special distributor construction involving insulationdifficulties. Since the two transformers have the same constructionthere will be an equal division of the voltage applied across theprimary windings before spark gap breakdown occurs. With thisarrangement should one only of the two gaps in a cylinder break down anda rapid succession of sparks begin in the one gap and not in the other,the resulting decrease in impedance of the secondary circuit supplyingsaid one gap, the gap being then ionized, immediately would cause amaterial decrease in the voltage drop across the corresponding primary.Consequently nearly the entire voltage of the source would then appearacross the other primary, raising the voltage of the other secondaryuntil the other gap breaks down and the succession of sparks beginsthere also.

It should be noted that not only does substantially the entire voltageof the generating source appear at the transformer whose secondary isnot conducting, but this voltage is maintained at its no load valuebecause there can be no large flow of primary current when only onesecondary is conducting. This is due to the fact that the no loadimpedance of the primary of the transformer whose secondary is notconducting is imposed in the circuit. As. soon as both spark gapsconduct, the current is limited primarily by the impedance of the supplycircuit.

While as stated above the source of alternating current voltage maycomprise any suitable and well known means, various means such as thoseincluding electron discharge tube oscillators having been successfullyused for this purpose, I have found it convenient to employ a generatorhaving an inductive winding such, forexample, as the dynamotor describedabove. With such a generator the inductance of the winding suppliessubstantially all the necessary circuit impedance for limiting the flowof current to the spark gap.

By another feature of my invention I am able to cause an automatic risein the voltage applied to the transformers l4 and I5 when thesecondaries thereof are not conducting. This I accomplish by connectingthe capacitor 23 across the primaries of transformers I 4 and I5, whichcapacitor has an impedance which is no greater but preferably somewhatless than the magnetizing or no load impedance of the transformers I 4and 15. -When the transformer secondaries,

ing two transformers l4 and IE, it will be understood that the samephenomenon would take place if a single transformer were employedinstead of two transformers as illustrated and a single gap employed ineach cylinder.

5 In Fig. 2 I have illustrated a singletransformer construction whichmay be substituted for the two separate transformers illustrated inFig. 1. As shown in Fig. 2 the transformer has a single core structure25 in the form of a figure 8 pro-' 10 vided with the two primarywindings 26 and 21 wound in the same direction and provided with the twosecondary windings 28 and 29.

In Fig. 3 I have shown a further modified form of transformer which hasa single core structure 30 somewhat like that shown in Fig. 2 but whichhas a single primary winding 3| on the central leg of the core and thetwo secondary windings 32 and 33 on the other two legs.

I have shown the particular embodiment described as illustrative of myinvention and it will be apparent that various modifications may be madewithout departing from the spirit and scope of my invention whichmodifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

'1. A multi-spark ignition system for an internal combustion enginehaving a spark gap comprising an inductive source of alternatingcurrent, a transformer having its primary connected in circuit with saidsource and its secondary connected with said spark gap and a capacitorconnected across said primary, the impedance of said capacitor beingsubstantially no greater than the 3. A multi-spark ignition system for amulticylinder internal combustion engine having a plurality of cylinderseach provided with a plurality of spark plugs comprising a highfrequency alternating current generator having an inductive generatingwinding, an engine operated switch, a plurality of transformers, meansconnecting the primaries thereof in a series circuit with said windingand switch, means for connecting the secondaries of said transformerseach with one spark plug in each cylinder and a capacitor bridged acrosssaid primaries, said capacitor having an impedance less than the no loadimpedance of said transformers.

4. A multi-spark ignition system for an internal combustion enginehaving a spark gap comprising an alternating current generator having aninductive winding, a switch, a capacitor, a transformer having itsprimary connected in a series circuit with said generator winding, saidswitch, and said capacitor, means connecting the secondary of saidtransformer with said spark gap and a capacitor bridged across saidprimary.

5. A multi-spark ignition system for a multicylinder internal combustionengine having a plurality of cylinders each provided with a plurality ofspark plugs comprising a high frequency alternating current generatorhaving an inductive generating winding, an engine operated switch, acapacitor, a plurality of transformers, means connecting the primariesthereof in a series circuit with said winding, said switch andsaidcapacitor, the capacitance of said capacitor being such that theseries circuit is resonant at a frequency corresponding to a speed lessthan the normal operating speed of the generator, means connecting thesecondaries of said transformers each with one spark plug in eachcylinder and a capacitor bridged across said primaries, said lastmentioned capacitor having an impedance less than the no load impedanceof said transformers.

BERNARD M. CAIN.

